Pig heart tissue activator of plasminogen has been purified from fresh pig heart to greater than 100,000 CTA units/mg protein. Polyacrylamide gel electrophoresis of preparations of this specific activity reveals the presence of only one major band and two minor bands. Plasminogen activating activity has been shown, by fibrin plate analysis of sliced gel, to be associated with the major band. Efforts will be made to remove these minor components by further purification by ion-exchange or affinity chromatography. The physico-chemical properties of tissue activator are to be studied. The molecular weight by gel filtration and SDS-polyacrylamide gel electrophoresis will be determined. Since little information exists as to the enzymatic characteristics of tissue activator, studies of the substrate specificity of tissue activator and the nature of the active site will be undertaken. It is expected that an antiserum to pig heart tissue activator will be available, and immuno-chemical studies will be carried out to determine if the blood activator is derived from tissue activator. During the proposed project period, purification of tissue activator from human tissues will be initiated, employing the separation techniques developed for purification of pig heart tissue activator.